Method of fabricating coils



March 22, 1960 M. WOHLHIETER 2,929,132

METHOD OF FABRICATING COILS Filed May 19, 1953 FIG.

M. WOHL HIE TER METHOD OF FABRICATING COILS Marion Wohlhieter,Livingston, N.J., asslgnor to Bell Telephone Laboratories, Incorporated,New York, N.Y., a corporation of New York Application May 19, 1953,Serial No. 356,041

2 Claims. (Cl.29155.57)

This. invention relates to miniature inductive devices and moreparticularly to electrical terminals and their attachment to suchdevices.

In order to accomplish the objective of miniaturization of coils andtransformers it is eminently desirable that simplified terminalassemblies and methods of terminal attachment be used. With thedevelopment of such inductive devices which may have a total volume of0.05 cubic inch or less and employed wire in the order of 40 gauge orsmaller, the attachment of terminals becomes a major problem. Use ofconventional terminals and attachment methods fails to gain the spaceadvantage possible with these minute devices and may leave the fragilewinding wire exposed. Improved reliability of the terminal connectionsis essential, first, because of the difiiculties in repairing devices ofsuch small size, and secondly, because many miniature coils andtransformers are potted or cast in resin so that a failure of a singleterminal connection results in complete loss of the component.

An object of this invention is to realize an inexpensive reliableterminal connection for miniature inductive devices.

Another object of this invention is to enable a simple, efiicientattachment of such terminals to miniature in- ..iuctive devices.

A further object of this invention is to expedite the attachment ofterminals to miniature inductive devices without increasing the size ordecreasing the efliciency of the device. '5 1 I .w

Still another object of this invention is to insure freedom from strainof fragile windings of components both during and after terminalattachment.

One embodiment of this invention includes a spool or bobbin type coilform including fusible spool heads on each side of a central hub aboutwhich the turns of the coil are wound. The terminals are comparativelyrigid wires extending parallel to the axis of the coil form and throughthe fusible spool heads.

Each terminal includes a bow or kink adjacent the winding, to which theinitial or final turn is soldered. The bow of the inner terminal liesagainst the coil form while the corresponding kink of the outer terminallies against the outer layer of the winding. A free length of windinglies within each bow, allowing some relative movement between theterminal and the coil without introducing undue tension into the coilwire. The entire winding assembly, including the bow portion of theterminals, is covered with a turn or two of pressure sensitive tape orthe device potted or cast in resin to secure the winding and terminals.The connection between the ends of the coil and the terminals arecompletely with in the device so not subject to damage due to abrasionor rough handling.

The terminals are attached in accordance with this invention byinserting each one, when heated, through the fusible spool heads,forming an upright bow or kink in the portion of the terminals lyingbetween the spool 2,929,132 Patented Mar. 22, 1960 ice ' minal andturning the terminals to lie one against the bobbin and the otheragainst the winding.

A feature of this invention involves the mounting of a terminal byinserting it through fusible portions of a coil form.

Another feature of this invention lies in the attachment of the terminalleads to the winding of inductive devices at a bow portion of eachterminal where soldering may be readily accomplished without danger tothe winding or insulation and which subsequently prevents rotation ofthe terminal.

' Still another feature of this invention relates to the formation ineach end of the winding a free length or loop soldered to and enclosedby a portion of the terminal.

A full understanding of these and other features of this invention maybe had from the following detailed description with reference to theaccompanying drawing in which:

Fig. l is a view in perspective of an inductive device embodying thisinvention with portions broken away for clarity;

Fig. 1A is a magnified view of the terminal-winding attachment detail ofthe device of Fig. 1;

Fig. 2 is an elevational view of a coil bobbin with one terminalattached and the initial turn of the winding in position for solderingto the terminal;

Fig. 3 is a perspective view of a portion of the bobbin of Fig. 2 withone terminal and the initial turn of the winding in place; and

Fig. 4 is a sectional view of the terminal detail of the I device ofFig. 1 taken along line 44.

Referring now to Fig. 1 an inductive device may be seen generallydesignated as coil 10 which includes a bobbin 11, winding12, and a pairof terminals 13 and 14. The bobbin 11 includes a tube 15 of insulatingmaterial, such as, paper, upon the ends of which are mounted a pair offlanges 16 of a fusible or thermoplastic material, such as, celluloseacetate. The flanges 16 may be punched from a sheet of cellulose acetateand press-fit over the ends of the tube 15 or the entire bobbin 11 maybe a single thermoplastic resin unit. Inner terminal 13 extends throughboth flanges 16 and along tube 15. The initial turn of the winding 12 issoldered to terminal 13 as is best seen in Figs. 2 and 3. The final turnof the winding 12 is soldered to the outer terminal 14 which, similar tothe inner terminal 13, extends through both flanges 16. Both terminalsinclude a bow or kink 17 in the section lying between the flanges 16.The ends of the winding 12 are each soldered to the apex of the bow ofterminals 13 and 14 which lie against the periphery of the tube 15 andthe winding 12, respectively. A turn or two of pressure sensitive tape18 surrounds the outermost turn and terminals securing both frommovement.

Referring now to Figs. 2, 3 and 4, the method of attaching this terminalto inductive devices may be more clearly understood. The terminals 13and 14 may include a preformed bow or kink or that partmay be formed inthe terminal after it is mounted on the coil bobbin. In either case theterminal is heated to a temperature suflicient to pierce the fusibleflanges 16. If the bow 17 is preformed, the terminal is inserted withthe bow upright, that is, extending radially from the tube 15. If astraight terminal wire is used, it is bent after insertion and coolingto form an upstanding bow, as seen in Fig. 2. Although either a straightterminal wire or one including a preformed bow may be inserted throughthe flanges 16 in accordance with this invention, it has been found thatthe straight wire offers less resistance to insertion, does not form aninternal burr on the flanges which in some cases must be removed beforeproceeding with the winding process and therefore is preferred.

After the inner terminal 13 with its upstanding bow 17 is insertedthrough the flanges 16, an end of the winding wire is stripped ofinsulation, looped about the bow 17 and soldered in place. Theterminal13 is then turned toward the winding direction until it lies against thetube 15. As the terminal is turnedit forms a bight 19 of winding wirewhich falls within the terminal bow. A strip 2%) of pressure sensitivetape is laid overthe terminal 13 and bight 1? and the requisite numberof turns of winding is wound about the bobbin 11 and terminal 13. Theouter terminal 14 is then heated and inserted through bothfianges in thesame manner as was used for the terminal 13;.however, it isadvisable toapply a strip 21 of pressure sensitive tape between the outer layerof-the winding "12 and the terminal 14 to protect the windinginsulation. Aftcrinsertion of terminal 14 and formation of the bow 17,the outer :end of winding 12 is stripped of insulation and'looped aboutthe apex of the bow or kink '17 and soldered thereto. The outer terminal14 is thenturned opposite of the direction of winding to form a bight22. 'In turning terminal 14, a bight 22 falls within the bow 17. Aturnor two of pressure sensitive tape 18 is laid over the entire windingassembly. The device may readily be potted or cast in aresinousmaterialif a hermetic seal is desired. In such a case the outer turns oftape may prove unnecessary.

The terminal of this invention hasjthe advantage of being simpleindesign and equally simple in attachment to inductive devices, Noauxiliarymounting member is required, for each terminal is fuseddirectly to the bobbin.

Furthermore, thebow or kink portion ofiers a readily accessible pointforsolder in the winding ends. Accessibility for soldering is an extremelyimportant factor of such devices which may have agreatest dimensionin'the order of three eighths of "an inch; Turning the terminals afteris formed and enclosed within the kink of the terminal wire, winding aseries of turns of the winding wire about the bobbin, rotatably securinga second terminal wire to an end flange of the bobbin including aportion of the terminal wire extending through the end flange into thewinding area of the bobbin, forming an upright kink in the portion ofthe second terminal wire extending through the end flange, connectingthe second end of said winding wire to the upright kink of said terminalwire, and rotating'said second terminal wire in the direction oppositeto the direction of winding while temporarily restraining all but'a freelength adjacent to the terminal wire of'the final turn of said windingto form a strain.

pair of spaced thermoplastic flange portions compris ng heating a firstterminal wire to at least the fusion temperature of said fiangeportions, inserting the first heated terminal through one of saidfusible thermoplastic flange portions of the coil bobbin along saidwinding area and into the other of said fusible flanges, forming anupright attachment .ofthe windingtothe bow portions, forms a t bight orloop which constitutes a'shortfree lengthof the winding between theturns and each terminal. This free length of the'winding allowssomemovement of the terminal both duringmanu facture and afterwardswithout danger of rupturing the winding. This free length of windingalso allows the'device tobe suspended by its terminals in a mounting-ora mold forencapsulation without endangeringthe winding. 7

'It is to be understood'that'the above-described arrangements'areillustrative of the applicationof the principles of the invention.Numerous other arrangementsmay b'e devised by'those skilled in the artwithout departing from thespirit'andscope -of the invention;

What is claimed is:

1. The method offabricating strainrelieving terminal connections tofragile windings of bobbin wound'electrical components comprisingrotatably' securing a first ter minal wire to'at leastoue'end flange ofa bobbin'including a portion of the terminal wire'extending through theend flange into the winding area of the bobbin,forming an 'uprightkinkinapor'tion of the terminal wireextending through the end flange,connecting an endof the fragile winding to the upright kink of saidterminal wire, rotating said terminal wire in the direction of thewinding while temporarily restraining all but-a free length adjacent to'said terminal wire of the first turn of said windkink in said terminalwire between said flange portions, attaching an'initial turn of awinding to the apex of said kink, turning said terminal in the directionof winding of said initial turn so the kink lies against said bobbinwhile temporarily restraining all but a free length adjacentto-saidterminal wire of the initial turn of sai d coil whereby saidterminal encompasses'an untensioned strain relief portion of the initialturn of said'coil, wind-' ingaceilabout said bobbin and terminal,heating a sec- .ond terminal wireto at least the fusion'temperature-ofsaid fusible flanges, insertings'aid second heated terminal Wire throughone of said flange portions over said coil :intoth'e' second of saidfusible flanges, forming-an up- 7 right kink in said second terminalwire between said flange portions, attaching the final turn of said coilto the apex of said kink, and turning'said second terminal wirein' thedirection opposite to the direction of winding of the coil whiletemporarily restraining all but a free length adjacent to said secondterminal wire of final turn of: said coil so the kink lies against theouterlayer'of'said series of turns and said ternn'nal encompasses anuntensioned-strain relief portion of the final turn of said coil.

References Cited in the file of this patent UNITED STATES PAT ENTS I MMa,

